1. Field of the Invention
This invention relates to a shutter control device for a camera provided with two separate latches to hold the closing member of the shutter in a charged position.
2. Description of the Prior Art
It has been common practice in the prior art, an example of which is depicted in FIGS. 1(a) and 1(b), to latch the shutter of the camera in such a way that, as the camera is being cocked, a charge pin 72' fixed to a gear 41' for a closing or second curtain is turned by a cutout pin 24' fixed to a gear 23' for the opening or first curtain, until it finally reaches the charged position illustrated in FIG. 1(a). A latch lever 25' for the first curtain engages the cutout pin 24' on which the second curtain charge pin 72' abuts, whereby both the first and second curtains are held. It should be noted in connection with this position that there is a prescribed clearance .alpha. between a release pawl 43' of a lever for the second curtain and a second curtain run-off plate 42'. Because of the presence of this clearance .alpha., the prior art devices have presented certain problems.
When the shutter is actuated to release from the charged position, the first curtain latch lever 25' is taken out of engagement with the cutout pin 24' to start movement of the first curtain. Though, at the same time, the second curtain is also rendered operative, the run-off catch plate 42' comes into engagement with the latch lever 43' so that the second curtain is held in the position of FIG. 1(b). After that, the second curtain release lever 43' is disengaged from the second curtain run-off catch plate 42' and the second curtain starts to run in accordance with a predetermined shutter time. As the cutout pin 24' moves away from the charge pin 72', the second curtain run-off catch plate 42' is driven by a spring (not shown) to move into abutting engagement on the latch lever 43' which produces a shock. From this moment onwards, the second curtain latch plate 42' or lever 43' vibrates with small amplitudes for a short time (for example, a few milli seconds). In the case of faster shutter speeds, for example, 1/4000 and 1/2000 sec., before this vibration is damped to zero (at a time during the vibrating process) the second curtain run-off catch lever 43' must be actuated. Therefore the formation of the exposure time becomes unstable so that the exposure time varies for different exposures causing uneven effects in the operation of the camera. The timing of the production of the vibration thus produced is illustrated in FIG. 2.
Since, at the same time, the predominance of the uneven operation makes it impossible to narrow the target for adjustment of faster shutter speeds in the assembly of the cameras, preadjusting has been a very difficult operation. Also, since with mass production there occur minute differences in the weight of the shutter mechanism, the strength of the shutter drive spring, and the friction of the finished surfaces of the moving parts, the vibration mentioned above will vary from shutter to shutter, and, in extreme cases, a situation could occur where faster shutter speeds cannot be preadjusted to the design values desired.
Further since the application of treatment to extend the life of the parts causes the frictional coefficient of the moving system to change, the state of the vibration changes with deviation of the faster shutter speeds from required tolerances, and the uneven operational effect is intensified.
As has been mentioned above, the conventional shutter latching mechanism has had various drawbacks with regard to the accuracy of shutter control.
It is, therefore an object of the present invention to eliminate the above-described drawbacks, and to provide for the closing member of the shutter with a release control or first latch and separately therewith a second latch, wherein after actuation of a camera release operation and before the opening member of the shutter runs off, disengagement of the second latch is released to effect engagement of the first latch with the closing member of the shutter, whereby the time of the occurrence of vibration of the shutter closing member run-off mechanism is advanced.
Another object of the present invention is to provide a camera having a mechanically timed shutter with an electromagnetic actuating device for controlling the operation of the closing member of the shutter to provide an electrically timed shutter, whereby the latch member of the electrically timed shutter may serve as the second latch.